1. Field of the Invention
The invention relates to determining densities and proportions of phases in a multi-phase fluid flow (MFF) that can include an oil phase, a water phase, and a gas phase from a well. The invention also relates to using the densities and proportions of the phases with flow sensors to determine the quantity output of the phases.
2. Discussion of Prior Art
Measurements of the outputs of oil and gas wells require a measurement system that accounts for the individual components of a multi-phase fluid flows (MFFs). The individual components include a gas phase, a water phase, and an oil phase. In some measurement systems, the different phases are separated and individually measured to determine the proportions between the phases and the output quantities, in volume or mass, of the phases. However, separation is an expensive process that is not cost effective for smaller land based wells that produce smaller quantities of energy. Alternatively, phase mixer-homogenizers are used as a less expensive alternative to separators when measuring the outputs of a MFF coming from a well. Phase mixer-homogenizers reduce the complexity of the mathematical equations used in calculating the output measurements of the phases by reducing the number of variables in the output equations. For example, when the three phases of gas, oil, and water come from a well they are usually partially separated in what is called a slug flow or stratified flow with the gas phases traveling quickly and slowly flowing liquid phases. To measure the flow rate of this type of separated MFF, the velocity of each phase has to be individually measured. However, a phase mixer-homogenizer creates a blended flow or uniform MFF with all of the phases traveling at the same velocity or flow rate. Therefore, with a phase mixer-homogenizer only one flow rate has to be measured because all of the phases travel at the same velocity. In contrast, with a separator three different flow rates need to be measured.
Density measurements of the different phases are important when solving for the outputs of the different phases from an oil or gas well. The density measurements are used to calculate the proportions between the different phases of gas, oil, and water. For example, density measurements are used to calculate the gas volume fraction of the MFF which is the proportion of gas in the MFF. Density measurements are also used to calculate the water cut of the MFF which is the ratio of water to oil in the MFF. These proportions can be combined with the single flow rate of the blended mixture of the MFF, from the output of the phase mixer-homogenizer, to determine the quantity outputs of the gas phase, the water phase, and the oil phase.
Additionally, density measurements are used to determine the proportions of phases even when the proportions are not used with flow rates to solve for the output quantities. The proportions of the different phases are used by the oil and gas industry to adjust different production inputs for oil and gas wells to optimize the production of the individual well or to optimize the production of an entire field of wells. Inputs into gas and oil wells may include: pressure, quantity of water input into the well, and the energy expenditure in pumping. Thus, density measurements of oil and gas wells are also an important because phases proportions alone, without flow metering, are useful for optimizing inputs into oil and gas wells.
However, traditional MFF density meters are too expensive to be used continuously with most small to mid-sized oil and gas wells that are land based. Therefore, traditional MFF density meters are configured as portable units to be used with multiple oil wells. This requires a crew to attach and move the density sensors, and thus portable density sensors increase labor expenses. Traditional MFF density meters also emit radiation, including X-rays and gamma rays. Additionally, traditional MFF density meters are only attached to an oil well periodically, usually with an interval of months between measurements. Changes in the outputs of an oil well or oil field, such as changes in proportions of phases, are not readily detected in these situations due to the long periods between density measurements on the wells. Frequent density measurements are necessary to determine changes in the phase proportions which are used to optimize production inputs of the oil well. Frequent density measurements also improve the accuracy of the quantity outputs (e.g. volume or mass) of the different phases because frequent density measurement accounts for changes in the proportions between the phases which affect the accuracy of the output quantity calculations. Many smaller output land based oil wells could use an inexpensive, non-radiation emitting, and permanent meter for measuring MFF densities to detect changes, thus increasing the ability to optimize production from an oil well, make fast business decisions, while also increasing safety.